There have been known apparatus and methods for sorting defective items from acceptable items by using machine vision techniques. Defect sorting systems based on such techniques have been commonly applied in the food product industry for the removal of fruits or vegetables containing defects. U.S. Pat. No. 5,085,325 of Jones et al. for COLOR SORTING SYSTEM AND METHOD, assigned to the assignee of the present invention, describes one such sorting system having a color camera for inspecting items as they are moved or propelled through an inspection zone by a conveyor belt. Color video data from the camera are digitized and used to address a lookup table containing criteria representing acceptable and rejectable colors. When the camera detects an item having a defect color, the defect location is stored in a memory for subsequent rejection of the item downstream of the camera. Conveyor belts typically move with sufficient speed to propel items off the end of the belt where a bank of air ejectors, triggered in response to stored defect data, are positioned to deflect defective items toward a rejection conveyor, while allowing acceptable items to fly undeflected toward an acceptance conveyor.
Such a system is quite effective at detecting the color, size, and location of defects in items. However items are often defective over only small portions of their surfaces. This creates an ejection efficiency problem for the air ejectors. Conventional defect sorting systems direct an air ejector blast at the detected location of a defect. For example, U.S. Pat. No. 4,276,983 of Witmer for SORTING APPARATUS describes a potato sorting system that includes a compressed air jet for deflecting defective potatoes into a reject bin. In such a system, when the air blast is directed toward a defect located at the edge of the potato slice, its trajectory may be insufficiently altered to deflect it toward the rejection conveyor. In some instances the air blast will cause the defective potato slice to spin toward the acceptance conveyor, often "bumping" acceptable items toward the rejection conveyor.
An item may also contain multiple defects. Conventional sorting systems direct an air blast at each defect location causing redundant operation of the air ejectors that leads to excessive wear and reliability problems. Moreover, the resulting excessive air blast can itself be deflected by the defective item toward an adjacent acceptable item causing its inadvertent rejection.
What is needed, therefore, is an apparatus and a method for improving the ejection efficiency of items containing non-centered or multiple defects.